Device and method for removing irregularities in or enlarging an underground duct

ABSTRACT

A device for removing irregularities in or enlarging a buried duct comprises a cylindrical housing corresponding approximately in diameter to the required diameter of the duct, an expandable shell comprising a plurality of tapered leaf members pivotally attached at their rear ends to the front of the housing, and remotely controllable drive means for moving the leaf members between contracted and expanded configurations. In operation, the apparatus is drawn through the duct with the leaf members in a contracted configuration in which they enter a portion of the duct of a diameter less than the required diameter. The drive means is operated to force the leaf members outwardly against the sides of the duct to expand the duct. The leaf members are then retracted and the apparatus is drawn forward. The apparatus is particularly intended for preparing damaged sewers prior to fitting an inner, lining pipe.

This application is a continuation of U.S. patent application Ser. No.679,671, filed Dec. 10, 1984, now U.S. Pat. No. 4,657,436, which is acontinuation-in-part of U.S. patent application Ser. No. 504,603, filedJune 15, 1983 (now U.S. Pat. No. 4,487,052).

This invention relates to a device for profiling an underground duct,for example an underground sewer which is to be repaired by fitting aninner pipe lining.

In many of the developed industrial countries of the world, undergroundsewers have to a large extent reached an age at which they are in astate of severe disrepair and liable to collapse. One method ofrepairing sewers is to line the existing sewer pipe internally withplastics pipe sections or an expandable plastics sleeve. However, thecondition of the original sewer is often such that the originalearthenware pipe sections are displaced relative to each other or havealready partly collasped. In these circumstances the diameter of aninner pipe lining made up of rigid plastics pipe sections is limitedover the length of sewer being repaired to that determined by the worstirregularity in that length. The result is that the flow capacity of therepaired sewer may be considerably reduced. Attempts have been made tohammer out the irregularities with a remotely controlled machine, butthis has proved difficult to control and can worsen the state ofcollapse.

It is an object of this invention to provide apparatus able largely toenlarge or correct the irregularities in an existing sewer in arelatively controllable and reliable manner.

SUMMARY OF THE INVENTION

According to a first aspect of this invention, apparatus for travellingthrough an underground duct and for removing irregularities in orenlarging the duct comprises an expandable segmented shell including aseries of shell parts arranged around a longitudinal axis of theapparatus and having respective outwardly facing surface portions forengaging the sides of the duct, and a trailing portion extendingrearwardly of the expandable shell in a longitudinal direction andhaving a diameter equal to or approaching a required duct diameter,wherein the shell parts are drivable laterally with respect to the axisfrom a contracted configuration in which at least front end portions ofthe shell parts lie within a duct penetration diameter, to an expandedconfiguration for driving the sides of the duct away from the axis tocreate a space within the duct of a diameter sufficient to receive thesaid trailing portion when the apparatus travels forward in the duct.

In a preferred embodiment of the invention, the apparatus of the subjectinvention the trailing portion has a generally cylindrical outer surfacecorresponding substantially to the required diameter of the duct, andhousing a longitudinally mounted ram or rams and means attaching the ramto the shell parts so that operation of the ram causes the leaf membersto move outwardly or inwardly.

In another preferred embodiment, the attaching means comprises aplurality of connecting links having their opposite ends pivotallycoupled respectively to the shell parts and to driving means producinglongitudinal motion. In a particularly preferred embodiment, oneconnecting link is provided for each shell part and is coupled at oneend to a distal end of the shell part and at the other end to the pistonof a hydraulic ram, the outward stroke of the ram putting the link undercompression and thereby forcing the distal end of the shell part awayfrom the longitudinal axis, with the shell part pivoting about itsproximal end and where it is attached to the body member.

The trailing portion may include a lining pipe coupled behind the shell.

The ram referred to above may be hollow in the sense that it has anannular cylinder with concentric tubular inner and outer walls, and anannular piston sliding in the space between the walls. This allows thedevice to be provided with a central longitudinal passage for a chain orcable extending from a winch ahead of the apparatus, through theapparatus, and to the rear end of a lining pipe behind the apparatus,allowing the pipe, which may be in sections, to be drawn forward in theduct under compression.

According to a second aspect of the invention, apparatus for travellingthrough an underground duct and for enlarging or removing irregularitiesin the duct comprises an expandable segmented shell including a seriesof shell parts arranged around a longitudinal axis of the apparatus andhaving respective outwardly facing surface portions for engaging thesides of the duct, wherein the shell parts are movable laterally withrespect to the axis from a contracted configuration to an expandedconfiguration for forcing the sides of the duct away from the axis toenlarge a portion of the duct, and a nose portion extending in alongitudinal direction forwardly of the segmented shell portion andhaving an outer surface engaging the sides of the duct ahead of the saidsegmented shell portion. The nose portion may comprise a secondexpandable and segmented shell including a second series of shell partsarranged around a longitudinal axis and having respective secondoutwardly facing surface portions for engaging the sides of the duct,the shell part of the second series being movable transversely withrespect to the said axis between a contracted configuration and anexpanded configuration. The shell parts of both series preferably eachhave a front end and a rear end, the front ends of the shell parts ofthe second series are each coupled on a first diameter around a forwardpivot assembly by a plurality of respective forward pivot joints, therear ends of the shell parts of the second series are each coupled byrespective intermediate pivot joints to the front ends of the shellparts of the first series, and the rear ends of the shell parts of thefirst series to a base member on a second diameter which is larger thanthe first diameter. In this case internally mounted fluid drive meansare preferably coupled to the shell parts in the region of theintermediate joints, having a generally cylindrical outer surface whenin the contracted configuration, thereby defining the penetrationdiameter, and a forwardly tapering outer surface in a fully expandedconfiguration. This tapering outer surface advantageously correspondssubstantially in shape to the forwardly tapering outer surface of thefirst series of shell parts when in their contracted configuration, suchthat the portion of the duct expanded by the nose portion is shaped toreceive the whole length of the first series of shell parts, whilst atrailing part of the apparatus, which may or may not include the pipelining behind it, simultaneously moves into a substantially cylindricalduct portion created by the expansion of the first series of shellparts.

According to a third aspect of the invention, there is providedapparatus for travelling through an underground duct and for enlargingor removing irregularities in the duct, wherein the apparatus comprisesan expandable segmented shell including a plurality of shell partsarranged around a longitudinal axis of the apparatus and havingrespective outwardly facing surface portions for engaging the sides ofthe duct, and wherein the shell parts are drivable laterally withrespect to the axis from a contracted configuration, in which at least afront end portion of the shell lies within a duct penetration diameter,to an expanded configuration in which the shell defines a forwardlytapered outer surface portion. Such tapering may be produced by a shellhaving two shell portions each having a respective series oftransversely movable shell parts.

Method aspects of the invention include a method of removingirregularities in or enlarging an underground duct comprising the stepsof (i) locating in the duct apparatus having a front part including anexpandable shell portion comprising a plurality of shell parts arrangedaround a longitudinal axis and movable laterally with respect to theaxis between a contracted configuration in which at least a front endsection of the expandable shell portion lies within a duct penetrationdiameter and an expanded configuration defining a larger, required ductdiameter, and a rear part having a diameter greater than the penetrationdiameter and less than or equal to the required duct diameter, theapparatus being located in the duct with the shell parts in theircontracted configuration and penetrating a portion of the duct of lessthan the required diameter, (ii) driving the shell parts outwardly intotheir expanded configuration thereby forcing the sides of the duct awayfrom the axis to create an enlarged duct portion having a diameter atleast as great as the said required duct diameter, (iii) causing theshell parts to return to their contracted configuration and theapparatus to move forwardly in the duct whereby the shell partspenetrate a new portion of the duct of less than the required diameter,and (iv) repeating steps (ii) and (iii) to traverse a required ductlength. A lining pipe may be simultaneously fed into the enlarged ductas part of or as an addition to the apparatus referred to above, thepipe being towed from the front or pushed from behind.

According to a second method aspect, the invention includes (i) locatingin the duct on expansion device including a leading expandable shellportion and a trailing expandable shell portion, which portions compriserespectively leading and trailing sets of shell parts which are movablelaterally with respect to a longitudinal axis between a contractedconfiguration and an expanded configuration, the device being located inthe duct with the shell parts in their contracted configuration and theleading shell portion in an unexpanded duct portion, (ii) driving theshell parts into their expanded configuration to force the sides of theduct away from the axis to create an enlarged duct portion having afront section which is forwardly tapering and a rear section having anoverall diameter at least as large as the required diameter of the duct,(iii) causing the shell parts to return to their contractedconfiguration and the device to move forwardly by a distance such thatleading shell portion enters a new unexpanded duct portion, and thetrailing shell portion substantially occupies the said front section ofthe enlarged duct portion, and (iv) repeating steps (ii) and (iii) totraverse a required duct length.

In a preferred method, the apparatus or the expansion device aresubjected to a continuous forwardly directed force and the shell partsare reciprocated back and forth in a regular manner. In this way, theapparatus or device moves forward automatically on each contractionstroke. Providing a nose portion corresponding, at least in thecontracted configuration, substantially to the penetration diameterlargely prevents the inward collapse of the sides of the duct prior tomoving forward the apparatus or device.

The apparatus or device may be driven through the duct by repeatedlyoperating a hydraulic ram at an accessible location, the ram beingalternately connected and disconnected during each operating stroke to achain or wire connected to the device through the duct.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference toFIGS. 1 to 12 of the drawings in which:

FIG. 1 is a schematic view of two sections of an underground pipe whichhave become displaced relative to each other;

FIG. 2 is a perspective view of an embodiment of the device of thepresent invention with shell parts in an expanded configuration;

FIG. 3 is a cut away side elevation of the device of FIG. 2 with a ramhousing shown in section, and with shell parts again in their expandedconfiguration;

FIG. 4 is an end elevation of the device of FIGS. 2-3.

FIG. 5 is a side elevation of part of the device of FIGS. 2-4, showingthe shell parts in their contracted configuration;

FIG. 6 is a diagrammatic section showing means for applying a pullingforce to a chain at one end of an underground duct;

FIG. 7 is a schematic view of another preferred embodiment of thepresent invention showing the shell parts in the contractedconfiguration;

FIG. 8 is a cut away side view of FIG. 7 showing connecting linkscoupling the hydraulic ram with the distal end of shell parts;

FIG. 9 is a perspective view of another embodiment of the presentinvention wherein the segmented front section of device comprises twosets of shell parts;

FIG. 10A is a cut away side view of the device of FIG. 9 showing shellparts in a retracted configuration;

FIG. 10B is a view similar to FIG. 10A but showing shell parts in anexpanded position;

FIG. 11 shows an operative environment of the device shown in FIGS. 9-10in an underground duct; and

FIG. 12 shows an alternative expansion means for expanding the shellparts shown in FIGS. 9-11.

Referring now to FIGS. 2-5 of the drawings, one embodiment of thepresent invention comprises a cylindrical base member 10 which acts as ahousing for a longitudinally mounted double-acting ram 12. The diameterof the base member 10 corresponds approximately to the required internaldiameter of the duct so that the device can be positioned in the ductwith its longitudinal axis substantially coincident with the axis of theduct. Attached to to the front end of the base member 10 are six taperedshell parts in the form of leaf members 14 arranged in annular fashionsymmetrically around the longitudinal axis. Each leaf member 14 has apart conical outer surface 16 and is pivotally mounted at its rear,proximal end to the base member 14 so that it is pivotable about arespective transverse axis. The transverse axes together form a regularpolygon perpendicular to the longitudinal axis, in this case a hexagon.A generally conical expander wedge 18 is mounted on the piston rod 20 ofthe ram 12 for moving the leaf members 14 between a first, contractedconfiguration position (FIG. 5) in which the leaf members 14 form aconical shell, and a second, expanded configuration in which their outersurfaces 16 constitute a generally cylindrical shell forming acontinuation of the outer surface of the base member.

Guide rails 22 on the wedge 18 locate in channels 24 formed in theundersides of the leaf members 14, and the outer surfaces 26 of therails are engaged by rollers 28 trapped in recesses at the front ends ofthe leaf members 14. Each rail 22 has a flange 30 so that a pair ofstuds 32 (FIG. 4) fixed in each leaf member 14 and located under theflange retains the front end of the leaf member on the rail 22. It willbe appreciated that when the leaf members 14 are under load, as is thecase when the device is being drawn through the undersize or collapsedduct, or when the ram 12 is operated to force the duct wall outward,considerable inwardly and rearwardly directed forces 13 are exerted onthe leaf members 14, and in turn on the base member 10 through thepivoted connections at the rear ends of the leaf members 14. Theseforces are transmitted between a transverse, convex, part-cylindricalbearing surface 34 (Figure5) on the rear end of each leaf member 14, anda concave part-cylindrical bearing surface 36 (FIG. 2) of correspondingradius machined in an annular end portion 38 of the base member 10.

The end portion 38 has six such bearing surfaces 36 arranged in ahexagon around its perimeter. The leaf member bearing surface 36 isprovided by a transverse steel bar 40 (FIGS. 2 and 4) welded to the rearend of the respective leaf member. For each leaf member 14 two pins 42(FIG. 2 and FIG. 3) received in a bolt bored through the bar 40, locatein the eyes of two inclined bolts 46 (FIG. 3) secured in the endposition 38 of the base member 10. The pins 42 serve only to retain theleaf member on the base member 10; they are a loose fit in the bolteyes, the compression forces under load being transmitted through thebearing surfaces referred to above.

Hydraulic supply pipes 48 for the ram 12 pass through the end portion 38of the base member 10 and through the interior of the wedge 18. Chains50 for drawing the device through the duct are attached to the basemember 10 and pass through a pair of recesses 52 (FIG. 4) in the outersurface of the wedge 18, although in an alternative embodiment (notshown) the chains may be attached instead to the front end of the wedge18. Referring to FIG. 6, the chains 50 are fed along the duct to a driveram 52 mounted in a stationary frame 54 bearing against the side of, forexample, a manhole 56. To pull the apparatus through the duct, the ram52 is reciprocated back and forth repeatedly, the piston rod of the ram52 being alternately connected and disconnected with the chain 50. Aratchet device 58 holds the chain 50 in tension between each stroke ofthe ram 52. A pair of rams may be used in place of the single ram 52.

In operation the remotely controllable device shown in FIGS. 2-5 and thedrive mechanism shown in FIG. 6 act together as follows.

The remotely controllable device is positioned in the duct at thebeginning of the stretch to be traversed and chains 50 are passedthrough the duct together with the hydraulic supply pipes 48 to themanhold 56. The chains 50 are secured to the drive mechanism and thepipes 48 connected to external control means (not shown) in the vicinityof the manhole. With the leaf members 14 in the contractedconfiguration, the remotely controllable device is drawn along the ductso that the walls of the duct are forced into the surrounding soilwherever they intrude inside the diameter of the base member 10.Depending on the nature of the duct and the soil around it, the pullingforce which can be exerted by the ram 52 and the chain 50 may beinsufficient to draw the device past certain locations. This conditionis sensed at the control location by monitoring movement of the chains50 or the fluid pressure in the ram 52. To remove the obstruction, asignificantly larger compression force can now be applied to the wall ofthe duct by operating the ram 12. By maintaining tension in the chains50, the remotely controllable device will begin to move forward againwhen the leaf members 14 are retracted. Thus, by a continuation ofpulling and expansion steps the device is drawn through the ducteventually to the manhole 56, leaving a passage of a diameter sufficientto accept a plastics lining of required diameter. Conveniently, thedevice may be used to draw pipe lining sections behind it as itprogresses through the duct.

To allow fluids to continue to pass through the duct when the remotelycontrollable device is being used, the device may include a passageconnecting the front end to the rear end. In this case, the ram 12 maybe replaced by a plurality of rams spaced around the axis, leaving aclear axial passage through the device.

A preferred embodiment of the invention is illustrated in FIGS. 7 and 8of the drawings. The device comprises a body member 110 housing a hollowlongitudinally mounted ram 112, and a leading portion comprising aplurality of leaf members 114 pivotally connected at their rear orproximal ends to the body member 110. In FIGS. 7 and 8 the leaf members114 are shown in a contracted configuration. Each leaf member 114 ispivotally secured at its front or distal end to a connecting link 116which is in turn secured to a respective pivot pin 118 fixed to thepiston 120 of the ram 112. The position and length of the links 116, inparticular their connection to the piston 120 at a point `down-stream`of the distal ends of the leaf members 114, are such that expansion ofthe ram 112 forces the leaf members 114 transversely outwardly away fromthe longitudinal axis of the device to push back the sides in which thedevice is operated. The ram 112, and its piston 120 are hollow, thecylinder having an annular section interior space between coaxial innerand outer walls. The piston 120 is also of annular section so that anaxial passage 121 is available through the device for a chain or cable122 running from a winch (as shown in FIG. 6) to a plate or the likefitted across the rear end of a lining pipe (not shown) travellingthrough the duct behind the device. The axial passage 121 is enclosedthroughout the length of the device by a tube 123.

The device may incorporate electronic or mechanically actuated limitsensors (not shown) for sensing the fully expanded and contractedconfigurations of the piston 120, links 116, or leaf members 114 sothat, if required, the expansion and contraction of the ram 112 can becarried out automatically. Thus, by reciprocating the ram 112 at aregular rate and applying a continuous tension to the chain 122, thedevice can be drawn through a duct with the minimum of supervision ormanual control as previously explained with reference to FIGS. 1-6.

The use of pivotal links 116 avoids the sliding engagement of the leafmembers with, for example, a wedge member as described above withreference to FIGS. 2-5. Such sliding engagement can lead to jamming orbreakages if debris from the duct becomes lodged in the wedge mechanism.The pivotal link arrangement has the further advantage that the leverageexerated by the driving means increases as the leaf members move towardstheir expanded configuration; in other words, when the resistanceoffered by the wall of the duct is likely to be greatest, the ratio ofpiston movement is at its highest value.

A particularly preferred embodiment is shown in perspective in FIG. 9and in section in FIGS. 10A and 10B. In this embodiment the front partof the device is an expandable shell having two sets of shell parts inthe form of leaf members, these comprising (i) a first trailing set ofleaf members 130 attached at their rear ends to a cylindrical rear bodymember 110 by a set of circumferential rear pivot joints 142, and (ii) asecond, leading set of leaf members 132 each pivotally attached at theirrear ends to the respective front ends of the trailing leaf members 130by intermediate pivot joints 133, and at their front ends to a roundedfront end pivot assembly 134 carrying a number of circumferential frontpivot joints 135. Mounted in the body portion 110 is a longitudinalhydraulic ram 112 which in this example is annular, with an annularpiston 120, providing a central longitudinal bore. This bore allows acentral passage, defined by a tube 123, to be provided over the wholelength of the device to receive a chain 122. The piston 120 carries apivot block 115 which is, in turn, coupled by a plurality of radiatingconnecting links 116 to the intermediate pivot joints 133 for convertinglongitudinal motion of the piston 120 into lateral (with respect to thelongitudinal axis of the device) motion of the front ends of thetrailing leaf members 130 and the rear ends of the leading leaf members132. The two sets of leaf members thus form an expandable shell having aleading portion constituting a nose portion for penetrating andexpanding an unenlarged duct portion, and a trailing portion forsubsequently further expanding that duct portion to an overall diametersuch that the body portion can then move forwardly into the duct portionwithout further expansion of the duct sides.

In FIG. 9, the device is shown in its expanded configuration with thetrailing set of leaf members 130 forming an approximately cylindricalenvelope having a diameter at least as large as the diameter of the bodymember 110. The leading set of leaf members 132 form a generally conicalsurface which tapers forwardly from a diameter at least as large as thatof the body member 110 to a smaller penetration diameter at the extremeforward end of the device. In the contracted configuration, the trailingleaf members 130 form a similar forwardly tapering conical surfacewhilst the leading leaf members 132 form a cylinder of the smallerpenetration diameter. The fully contracted and expanded configurationsare shown more clearly in FIGS. 10A and 10B respectively, which aresectional views.

The split front part of the device shown in FIGS. 9-11 has particularadvantage in the enlargement of a duct. As illustrated in FIG. 11 wherethe device is shown in side elevation, the leading leaf members 132 intheir contracted configuration are able to penetrate an original duct140 of diameter D₂ which is larger than the penetration diameterreferred to above but smaller than the diameter of the body member 110.The device is being used to enlarge the original duct 140 to a requireddiameter D₂ corresponding to the diameter of the body member 110, and atthe same time, for drawing a pipe lining 144 of similar diameter throughthe duct behind it. With a continuous tension applied to the chain 122(attached to the rear end of the lining 144 to place the joints betweenthe sections of the lining under compression), the ram 112 (FIGS. 10Aand 10B) is operated to expand the leaf members into the position shownby the dotted lines 142, forcing out the sides of the duct to the newdiameter D₂. Since the leaf members are all of approximately equallength the forwardly tapered profile of the expanded duct formed by theexpansion of the leading leaf members 132 corresponds to the forwardlytapered surface formed by the trailing leaf members 130 in theircontracted configuration. Thus, when the ram 112 is caused to retract,the whole device and the pipe lining 144 can move forward by a distance"S" which is the length of the leaf members. This means that in a ductenlarging operation a full length "S" of the duct can be enlarged witheach cycle of the ram 112. This is larger than the length that can beenlarged per cycle using the device of FIGS. 2-5 and 7-8, since thelatter allows only a limited penetration distance into the originalduct. In addition, the presence of the nose portion formed by theleading leaf members 132 reduces the possibility of the duct sidescollapsing ahead of the device during the expansion operation, becausethe front ends of the leaf members 132 merely engage the duct sides tostablise them without expanding them at that point.

Another embodiment of the invention is shown in section in FIG. 12. Inthis embodiment a split expandable shell is employed as in FIGS. 9, 10Aand 10B, but in this case a wedge expander 146 is coupled to the piston120 instead of pivotable connecting links to expand the leaf members 130and 132. This construction can be preferable when space is limited as ina device designed for relatively small ducts, typically 150 mm diameteror less.

In describing the invention, reference has been made to a preferredembodiment. Those skilled in the art, however, and familiar with thedisclosure of the subject invention may recognise additions, deletions,substitutions, modifications and/or other changes which will fall withinthe perview of the invention as defined in the following claims.

What is claimed is:
 1. Apparatus for travelling through an undergroundduct and for enlarging the duct or removing irregularities in the wallof the duct, wherein the apparatus comprises an elongate segmented shellarranged around a longitudinal axis of the apparatus and havingoutwardly facing surface portions for engaging the wall of the duct, anda trailing portion extending rearwardly of the shell in a longitudinaldirection and having a diameter equal to or approaching the requiredduct diameter, wherein the shell is expandable laterally with respect tothe axis from a contracted configuration in which at least a front endportion of the shell lies within a duct penetration diameter, to anexpanded configuration for engaging the duct well over an area thereofand driving the said area of wall away for the axis to create a voidwithin the duct for receiving the trailing portion when the apparatustravels forward in the duct.
 2. Apparatus according to claim 1, whereinthe apparatus includes internal fluid pressure drive means coupled tothe segmented shell for expanding the shell.
 3. Apparatus according toclaim 2, wherein the drive means comprises a longitudinally actinghydraulic ram.
 4. Apparatus for travelling through an underground ductand for enlarging the duct or removing irregularities in the wall of theduct, wherein the apparatus comprises an elongate segmented shellarranged around a longitudinal axis of the apparatus and havingoutwardly facing surface portions for engaging the wall of the duct,means for expanding the shell laterally with respect to the axis from acontracted configuration to an expanded configuration for forcing thewall of the duct away from the axis to enlarge a portion of the duct andfor creating a void in the duct when the shell is returned to itscontracted configuration, and wherein the shell further comprises aforwardly extending nose portion having an outer surface for engagingthe wall of the duct ahead of the area to be driven away from the axis.5. Apparatus according to claim 4, including internal fluid pressuredrive means coupled to the segmented shell for expanding the shell. 6.Apparatus according to claim 5, wherein the shell defines, in theexpanded configuration, an outer surface having a forwardly taperedfront surface portion and a cylindrical or rearwardly tapered rearsurface portion.
 7. Apparatus for travelling through an underground ductand for enlarging the duct or removing irregularities in the wall of theduct, wherein the apparatus comprises an expandable segmented shellarranged around a longitudinal axis of the apparatus and having anoutwardly facing surface portion for engaging the wall of the duct overa transversely and longitudinally extending area, and drive meanscoupled to the shell for driving said surface portion radially away fromthe axis thereby to move said duct wall area outwardly into thesurrounding material, and wherein, in the contracted configuration ofthe shell, at least part of said surface portion lies within a ductpenetration diameter, and in the expanded configuration of the shell,the surface portion forms part of a forwardly tapering cone. 8.Apparatus according to claim 7, wherein the shell defines, in theexpanded configuration, an outer surface having a forwardly taperedfront surface portion and a cylindrical or rearwardly tapered rearsurface portion.
 9. Apparatus according to claim 8 having, in thecontracted configuration of the shell, a forwardly tapered rear outersurface portion corresponding substantially in shape to said forwardlytapered front surface portion of the expanded shell.
 10. A method ofremoving irregularities in or enlarging an underground ductcomprising:(i) locating in the duct an expansion device including aleading expandable shell portion and a trailing expandable shellportion, which portions comprise respectively leading and trailing setsof shell parts which are movable laterally with respect to alongitudinal axis between a contracted configuration and an expandedconfiguration, the device being located in the duct with the shell partsin their contracted configuration and the leading shell portion in anunexpanded duct portion; (ii) driving the shell parts into theirexpanded configuration to force the sides of the duct away from the axisto create an enlarged duct portion having a front section which isforwardly tapering and a rear section having an overall diameter atleast as large as the required diameter of the duct; (iii) causing theshell parts to return to their contracted configuration and the deviceto move forwardly by a distance such that leading shell portion enters anew unexpanded duct portion, and the trailing shell portionsubstantially occupies the said front section of the enlarged ductportion; and (iv) repeating steps (ii) and (iii) to traverse a requiredduct length.
 11. A method according to claim 10, wherein a continuousforwardly directed force is applied to the device over a plurality ofcycles of steps (ii) and (iii).
 12. A method of lining an undergroundduct, including enlarging the duct as defined in claim 10, andsimutaneously feeding a lining pipe into the duct.
 13. A device forremoving irregularities in or enlarging an underground duct comprisingan expandable segmented shell having two sets of shell parts arrangedaround a longitudinal axis of the device, the two sets comprising afront set in which the shell parts are each pivotally attached by frontend portions thereof to a forward pivot assembly, and a rear set inwhich the shell parts are each pivotally attached by front end portionsthereof to rear end portions of respective shell parts of the front set,and by rear end portions thereof to a base member.
 14. A method ofremoving irregularities in or enlarging an underground ductincluding:(i) locating in the duct apparatus according to any of claims1, 4 and 7 with the shell in its contracted configuration; (ii) drivingthe shell radially outward to its expanded configuration to create anexpanded duct portion; (iii) returning the shell to its contractedconfiguration; (iv) causing the apparatus to move forwardly into theexpanded duct portion; and (v) repeating steps (ii), (iii), and (iv) totraverse a required length of the duct.
 15. A method according to claim14, wherein the expanded duct portion is forwardly tapered over at leasta part of its length.
 16. A method of enlarging or removingirregularities in an underground duct comprising:(i) locating in theduct apparatus having a front part including an expandable shell portioncomprising a plurality of shell parts arranged around a longitudinalaxis, and movable laterally with respect to the axis between acontracted configuration in which at least a front end section of theexpandable shell portion lies within a duct penetration diameter and anexpanded configuration defining a larger, required duct diameter, and arear part having a diameter greater than the penetration diameter andless than or equal to the required duct diameter, the apparatus beinglocated in the duct with the shell parts in their contractedconfiguration and penetrating a portion of the duct of less than therequired diameter; (ii) driving the shell parts outwardly into theirexpanded configuration thereby forcing the sides of the duct away fromthe axis to create an enlarged duct portion having a diameter at leastas great as the said required duct diameter; (iii) causing the shellparts to return to their contracted configuration and the apparatus tomove forwardly in the duct whereby the shell parts penetrate a newportion of the duct of less than the required diameter; (iv) repeatingsteps (ii) and (iii) to traverse a required duct length; and in which acontinuous forwardly directed force is applied to the apparatus over aplurality of cycles of steps (ii) and (iii).
 17. A method according toclaim 16, wherein the rear part of the apparatus comprises a liningpipe.
 18. A method according to claim 16, wherein the enlarged ductportion is forwardly tapered.
 19. Apparatus for travelling through anunderground duct and for enlarging the duct, wherein the apparatuscomprises an elongate segmented shell having a central longitudinal axisand including a shell portion which is movable radially outwardly awayfrom the axis toward the duct wall, drive means coupled to the shellportion to drive the shell portion radially outwardly from a contractedstate in which the shell portion lies within a duct penetration diameterto an expanded state thereby to engage a portion of the duct wall over acircumferentially and longitudinally extending area and to drive saidduct wall portion radially away from the axis to create a space intowhich a rear portion of the apparatus may move when moved forward in theduct.
 20. Apparatus according to claim 19 wherein the movable shellportion is generally part conical in shape.
 21. Apparatus according toclaim 19 wherein the drive means comprises a longitudinally andinternally mounted ram, and wherein the apparatus further includes meansconnecting the ram to the shell portion for converting a longitudinalmovement of the ram to movement radially of the axis.
 22. Apparatusaccording to claim 21 wherein the connecting means comprises a wedgeexpander.
 23. Apparatus according to claim 19 wherein the shell portionincludes hinge means at a forward end thereof.
 24. Apparatus fortravelling through an underground duct and for enlarging the duct,wherein the apparatus comprises an elongate segmented shell of generallycircular cross section having a central longitudinal axis and includinga shell portion which is movable radially outwardly away from the axisand which has a circumferentially and longitudinally extending surfaceportion for engaging a surface area of the duct wall, and an internalfluid-driven ram means coupled to the shell portion for driving theshell portion radially outwardly from a retracted state to force saidduct wall portion radially outwardly into material around the duct, theshell portion being arranged such that, in its retracted state, at leasta forward end of said surface portion lies within a duct penetrationdiameter and, in its extended state, the surface portion in alongitudinal cross-section is inclined towards the axis in the directionof travel, whereby movement of the shell portion from its retractedstate to its expanded state and back to its retracted state creates avoid to allow forward movement of the apparatus in the duct.